The present invention relates generally to techniques for compressing relatively large light intensity ranges and more particularly to different optical techniques for accomplishing this utilizing (1) photogray glass, (2) interference filters, and (3) a novel liquid crystal notch filter, the latter by itself being the subject of the present invention.
There are times when it is desirable to view an object having a relatively large light intensity range and record what is viewed by means of a camera or like instrument. For example, applicant has found a need to view the crucible containing molten uranium in an atomic vapor laser isotope separation (AVLIS). However, this molten uranium containing crucible functions as a black body having a center which is at a temperature of approximately 3800.degree. k and outer edges at temperatures on the order of 1000.degree. k. Thus, the temperature range across this black body is approximately 3000.degree. k. and has a correspondingly large light intensity range (9 orders of magnitude) which is much too large for a standard video (2-3 orders of magnitude) camera or like instrument to receive and decipher. Therefore, if standard viewing and/or recording equipment is to be used to view the crucible, its light intensity range must be compressed (1-3 orders of magnitude) which is a tolerable level.
The concept of compressing a relatively large light intensity range is not new. Heretofore it has been done electronically, that is, by converting the incoming light to corresponding electrical signals, compressing the electrical signals, and then converting those compressed electrical signals back to light which itself is compressed relative to the incoming light. Applicant has found this "electronic" approach to light compression to be relatively complicated and expensive.
To applicant's knowledge there has been no suggestion of compressing a light intensity range entirely optically, that is, by acting on the light itself rather than converting the light to electrical signals which are then compressed and converted back to light.